Field of the Invention
This application relates generally to acoustic sensor systems, and more particularly to optical-fiber-compatible acoustic sensor systems.
Description of the Related Art
Various fiber optic sensor systems have been previously disclosed that provide acoustic pressure measurements based on the relative displacements of the two mirrors of a Fabry-Perot interferometric cavity. See, e.g., M. Yu et al., “Acoustic Measurements Using a Fiber Optic Sensor System,” J. Intelligent Material Systems and Structures, vol. 14, pages 409-414 (July 2003); K. Totsu et al.,“Ultra-Miniature Fiber-Optic Pressure Sensor Using White Light Interferometry,” J. Micromech. Microeng., vol. 15, pages 71-75 (2005); W. B. Spillman, Jr. et al., “Moving Fiber-Optic Hydrophone,” Optics Lett., vol. 5, no. 1, pages 30-31 (January 1980); K. Kardirvel et al., “Design and Characterization of MEMS Optical Microphone for Aeroacoustic Measurement,” 42nd AIAA Aerospace Sciences Meeting and Exhibit, 5-8 Jan. 2004, Reno, Nev.; J. A. Bucaro et al., “Miniature, High Performance, Low-Cost Fiber Optic Microphone,” J. Acoust. Soc. Am., vol. 118, no. 3, part 1, pages 1406-1413 (September 2005); T. K. Gangopadhyay et al., “Modeling and Analysis of an Extrinsic Fabry-Perot Interferometer Cavity,” Appl. Optics, vol. 44, no. 16, pages 312-3196 (1 Jun. 2005); and P. J. Kuzmenko, “Experimental Performance of a Miniature Fabry-Perot Fiber Optic Hydrophone,” Proceedings of 8th Optical Fiber Sensors Conference, Monterey, Calif., Jan. 29-31, 1992, pages 354-357; O. Kilic, M. Digonnet, G. Kino, and O. Solgaard, “External fiber Fabry-Perot acoustic sensor based on photonic-crystal mirror,” in 18th International Optical Fiber Sensors Conference, Cancun, Mexico (2006); O. Kilic, M. Digonnet, G. Kino, and O. Solgaard, “External fibre Fabry-Perot acoustic sensor based on a photonic-crystal mirror,” Meas. Sci. Technol. 18, 3049-3054 (2007); O. Kilic, M. Digonnet, G. Kino, and O. Solgaard, “Photonic-crystal-diaphragm-based fiber-tip hydrophone optimized for ocean acoustics,” in 19th International Optical Fiber Sensors Conference, Perth, Australia (2008); O. Kilic, M. Digonnet, G. Kino, and O. Solgaard, “Fiber-optical acoustic sensor based on a photonic-crystal diaphragm,” in 15th International Conference on Solid-State Sensors, Actuators, and Microsystems, Denver, Colo. (2009).
Photonic-crystal slabs (PCSs) are photonic-crystal structures having a spatially periodically varying refractive index. A PCS exhibits guided resonance optical modes that are strongly confined within the PCS, but are coupled to incident radiation through a phase matching mechanism due to the periodically varying refractive index. These guided resonance modes are typically manifest in transmission or reflection spectra as sharp Fano lineshapes superimposed on a smoothly varying background. See, e.g., M. Kanskar et al., “Observation of leaky slab modes in an air-bridged semiconductor waveguide with a two-dimensional photonic lattice,” Appl. Phys. Lett., vol. 70, page 1438 (1997); V. N. Astratov et al., “Resonant coupling of near-infrared radiation to photonic band structure waveguides,” J. Lightwave Technol., vol. 17, page 2050 (1999); and S. Fan and J. D. Joannopoulos, “Analysis of guided resonances in photonic crystal slabs,” Phys. Rev. B, vol. 65, page 235112 (2002). Such guided resonance modes have been used previously as optical filters or mirrors in light emitting diodes and lasers